The present invention relates to an apparatus for controlling a semi-active suspension system; and, more particularly, to an apparatus for controlling a semi-active suspension system using a variable damping force type shock absorber, wherein the damping force characteristics in rebound strokes and in compression strokes are controlled independently by means of separate control valves and utilizing a magneto-rheological fluid.
In a semi-active suspension system for a vehicle, damping forces of respective shock absorbers are controlled independently by measuring the behavior of respective wheels by using, for example, vertical acceleration sensors installed at respective portions of the vehicle body adjacent to the shock absorbers.
As a control method for such a semi-active suspension system, the so-called xe2x80x9csky-hookxe2x80x9d method is usually employed. This control method works as follows: when the direction of a vehicular vertical velocity is upward with respect to a road surface, the damping force characteristic in rebound strokes becomes hard, i.e., the damping force becomes relatively large, whereas the damping force characteristic in compression strokes becomes soft, i.e., the damping force becomes relatively small; and when a direction of a vehicular vertical velocity is downward with respect to a road surface, the damping force characteristic in rebound strokes becomes soft or relatively small, while the damping force characteristic in compression strokes becomes hard or relatively large.
Conventionally, two types of shock absorbers are employed for the semi-active suspension system. One is a reverse type semi-active damper and the other a normal type semi-active damper. In a suspension system using the reverse type semi-active dampers, the xe2x80x9csky-hookxe2x80x9d control method can be applied by measuring vehicular vertical velocities only. However, the suspension system using reverse type semi-active dampers cannot offer an anti-roll control for preventing rolling behavior which occurs when a vehicle is steering. On the other hand, a suspension system using the normal type semi-active dampers can adopt the xe2x80x9csky-hookxe2x80x9d control method as well as prevent the rolling behavior. However, in this system, vertical velocities of axles as well as vehicular vertical velocities should be measured, requiring more sensors than the suspension system using the reverse type semi-active dampers.
In order to solve these problems, an apparatus and a method for controlling damping force characteristic of a vehicular shock absorber and two types of shock absorbers therefor have been disclosed in U.S. Pat. No. 6,092,011. In order to control the damping force characteristics of the shock absorbers, a first type shock absorber uses a control valve driven by a stepping motor while a second type shock absorber uses throttling mechanisms driven by solenoid valves. However, in such a configuration, the damping force characteristics do not change continuously and their response times are not fast enough, which give performance restrictions.
As a shock absorber which has continuous damping force characteristics and response times fast enough, magneto-rheological fluid dampers (MR dampers) have been proposed in U.S. Pat. No. 5,277,281. However, no control method is provided in this patent.
It is, therefore, an object of the present invention to provide an apparatus for controlling a semi-active suspension system using a variable damping force type shock absorber, wherein damping force characteristics in rebound strokes and in compression strokes are controlled independently and MR fluids are utilized.
In accordance with a preferred embodiment of the present invention, there is provided an apparatus for controlling a semi-active suspension system of a vehicle including at least one shock absorber using a magneto-rheological fluid. The shock absorber has a rebound valve and a compression valve which are configured such that damping forces of the shock absorber generated in rebound strokes and compression strokes are controlled independently of each other. The apparatus comprises a normal driving control unit for determining a ride value (Sride) as well as a filtered vehicular vertical velocity (vi) based on a vehicular vertical acceleration; an anti-roll control unit for determining a roll value (Sroll) based on a velocity and a steering angle of the vehicle; and a damping force adjusting unit for controlling the rebound valve and the compression valve of the shock absorber based on the roll value (Sroll), the ride value (Sride) and the filtered vehicular vertical velocity (vi) under a predetermined condition.
A shock absorber which has a configuration such as shown in FIG. 10(c) of U.S. Pat. No. 5,277,281 may be used for the apparatus for controlling a semi-active suspension system of the present invention.